1. Field of the Invention
This invention relates to error concealment in digital television signals.
2. Description of the Prior Art
If errors occur in the handling of digital television signals, for example due to noise or drop-out occurring in a digital video tape recorder (VTR), the digital signals are lost or corrupted, and then the reformed analog television signal does not correspond exactly to the original analog television signal, and a resulting picture is degraded.
There are two main approaches to dealing with errors in digital television signals. The first approach is correction, which involves the production and use of additional data signals purely for the purpose of error detection and correction, these additional data signals otherwise being redundant. While correction provides good results, it cannot generally be used as the sole means of dealing with errors, because a comprehensive correction capability would require an excessive amount of additional data which might overload the data handling paths or raise the data rate to an unacceptable level. The second approach, with which the present invention is more particularly concerned, is concealment. This comprises the replacement of lost or corrupted data signals by data signals generated using available uncorrupted data signals. This method relies largely for accuracy on the strong correlation that exists in a television signal.
In our UK Pat. No. 2,073,534 and the corresponding European Pat. No. 0,037,212, we have disclosed a method of error concealment which comprises selecting from a plurality of algorithms a preferred algorithm for calculating a corrected value for use in concealment of an error sample, calculating a corrected value for the error sample using the preferred algorithm, and replacing the error sample by the corrected value sample. This method works well in most situations, but we have found that there are certain error situations and also certain signal frequency conditions which result in problems in selecting the preferred algorithm. These problems will be discussed in more detail below.